diff --git a/src/main/java/org/apache/ode/jacob/vpu/ExecutionQueueImpl.java b/src/main/java/org/apache/ode/jacob/vpu/ExecutionQueueImpl.java
index da83d31..bb38f89 100644
--- a/src/main/java/org/apache/ode/jacob/vpu/ExecutionQueueImpl.java
+++ b/src/main/java/org/apache/ode/jacob/vpu/ExecutionQueueImpl.java
@@ -510,7 +510,7 @@
         public String toString() {
             StringBuffer buf = new StringBuffer(32);
             buf.append("{CFRAME ");
-            buf.append(type.getSimpleName());
+            buf.append(type == null ? "untyped" : type.getSimpleName());
             buf.append(':');
             buf.append(description);
             buf.append('#');